Dry dock pontoon construction



VD126- 17, 1946. F. R. HARRISl DRYDOCK PONTOON CONSTRUCTION Filed Aug.,'7, 1943 5 Sheets-Sheet l IN VEN TOR. i Frederic R; Harris v Dec. 17,T1946. F. R. HARRIS vDRYDOCK PONTOON CONSTRUCTION 5 Sheets-Sheet 2 FiledAug. 7, 1945 ii L SPM Dec. 17, 1946. F, R, HARRls 2,412,578

DRYDOCK PONTOON CONSTRUCTION Filed Aug. '7, 1943 5 sheets-sheet 4 b NIMHHIL En IMM F uw i is INVENroR. Frederic Jrns Arron/wav Patented Dec. 17,1946 UNITED STATES PATENT OFFICE 11 Claims.

This invention relates to the construction of hulls and especiallypontoon hulls for floating dry docks.

An important object of the invention is to prov-ide an improved internalframework for a dry dock pontoon, comprisingA a novel and advantageousarrangement of bulkheads and cooperating trusses.

The floating dry dock, adapted to lift a ship out of Water and properlysupport it for repairs, has undergone much recent development in keepingwith modern progress in the design of. ships. At rst amarine Vesselcomprised a shell. internally braced by transverse frames, rigidlyconnected to a central keel, which eX- tended over the vessels entirelength. Therefore, in a dock, the whole ship load couldk be supported onblocks directly under the keel, which was the strongest. part of theship.` Bilge blocks were added at the sides merely toV balance thevessel on the keel blocks.

The keel was afterwards replaced by a shallow double bottom Which,however, did notin any substantial manner change the. dockingconditions; and floating dry docks were: designed before to take theentire load on acentral row or track of blocks, which were still. oftimber and bore the full weight of the vessel without crush- But at thepresent day there are both. commercial and naval vesselsofv suchk greatsize and weight that, even shoulda continuous keel track be provided.kthe whole length of the dock, this track would have to be sobroadthatasubstantial portion of the ships bottom would be covered thereby andmade. inaccessible to workmen The remedy for this. is a plurality oftracks orv rows of blocks, side by side on the floor of thev dock; and astructural design for the dock-4 that is economical in the amount ofmaterial' used, and yet firm enough to withstand all working stressesdue to the vessels weight, and other forces.

In floating dry docks of` prior construction a rugged, centrallongitudinal bulkhead is usually included; with a considerable numberof' transverse bulkheads. My invention contemplates several bulkheadsfor carrying and sharing the weight of the ship; and: both the ship loadandthe buoyancy load are transmitted to said'bulkheads by a system offrame-trusses; andV thencet'o additional bulkheads which intersectYtheirst, and complete the framework of the hullof: the dock. The resultis great strength and. alargesaving in structural material.V

The invention will be described in. connection with a pontoon of amultiple-unit dry dock; that is, a dry dock that is made up of. a numberof similar pontoons connected together side by side to form alongdockfor supporting a ship; as set iorthin my application for patent on aMultipleunit floating dry dock, Serial No. 482,376, led April 9, 1943,noW Patent No. 2,37 9,904, dated July 10, 1945. But the invention is notlimited to pontoons of multiple-unit docks, and some features of theinvention relate to hull construction generally.

My invention' provides bulkheads arranged so as to extend crosswi'se ofa ship in the entire dock, and placed someV distance apart, and aseriesof trusses containing K frames on both sides of; each of saidbulkheads. Horizontal beam members-to resist compression extendfro'mside to side of the hull of the pontoon and unite the centers ofthe K frames inthe diierent trusses; and the frames at each side arefurther braced by beams. connecting their centers. Thus the trusses arestiffened in their various positions and, with their increased rigidity,are' able to support high compression loads. The span ofv the uprightsin the trusses becomes half of that in a' prior floating dry dock. Thehorizontal beam members in their turn, being joined rigidly'together,willrv resist eifectively the outsidey water pressures on the' sidesandends of the'ponto'on.

Also my invention rendersi it feasible to rely upon relatively fewbulkheads tonv transmit inherent pontoon truss-bending stresses. The Kframe. trusses which, at their ends are securedto some of the bulkheads,will, together' with the additional bulkheads and their plating betweenthe. trusses, render the whole interior framework so strong and rigidthat all liability of Warping andsimilar strains in thsbulkheadsiseliminated."

Also the trusses render the deck and bottom so rigid that the entiredeck and` bottom: plating willv act as flanges' for girders, thewebs of'which are formed by' they additional bulkheads; and buckling andother'distortionof deck and bottom plates .becomes impossible.

In addition, my invention-contemplates sufli cient additionalreinforcement in the central part of the pontoon. hull-tovcooperateiwith the bulkheads and trusses in realizing the fullf aim ofthe invention.

Another feature of the' invention relates to a combination ofbulkheadsand trusses within the pontoon by which loadszare transmittedto some bulkheads and. througlrthem. to.- additi'onal; bulkheads. Intheembodiment: of thefnventionillusitrated, the trusses and the`vvariousbulkheads 3 are all connected together to form a unitarystructure inside the hull.

A more specic object of the invention is to transmit deck load andbuoyancy loads through parallel K frame trusses to bulkheads at theopposite ends of the trusses, and from these bulkheads to additionalbulkheads within the pontoon connected to and intersecting the firstbulkheads.

A further feature of the construction is that the bulkheads are of acomposite structure that is thicker at the places where each bulkheadmeets another bulkhead extending in a transverse direction. Thisconstruction may comprise solid columns located where the planes of thebulkheads intersect, the respective bulkheads being made up of sectionsconnected with the solid columns in such a way that the column Aisstructurally a part of the composite bulkheads.

Dry dock pontoons made in accordance with this invention have a numberof bulkheads with parallel trusses between and on each side of thelatter, bulkheads at the opposite ends of the trusses and under the wingwall sections on the pontoon, and other trusses beyond the last namedbulkheads and less closely spaced. In this way the greatest strength isconcentrated under the portion of the pontoon deck that supports theship, and less strength is needed adjacent the ends of the pontoon wheresmaller stresses are encountered.

Some features of the invention relate also to the connection ofstructural members 'and to special joints that are particularly suitablefor welded connections in ship construction and other objects, featuresand advantages of the invention will appear or be pointed out as thedescription proceeds.

In the drawings, forming a part hereof, and in which like referencecharacters designate corresponding parts in all the views,

Figure l is an enlarged sectional view taken on the line iof Figure 2;

Figure 2 is a diagrammatic, top plan view of a pontoon hull for amultiple dry dock built in accordance with this invention;

Figure 3 is a perspective view of jointing elements used at certainjoints of the framing;

Figure 4 is an enlarged detail view illustrating the connection of someof the structural members shown in Figure 1;

Figures 5 and 6 are two enlarged sectional views taken on the lines 5-5and 6-6 respectively, of Figure 2 showing the construction of the sidetrusses;

Figure 7 is an enlarged, fragmentary perspective view taken in thevicinity of the line 'lf Figure 8; 1

Figure 8 is an enlarged, sectional view taken on the line 3-8 of Figure2 showing the structure of the other trusses;

Figure 9 is an enlarged. detail, perspective View taken on the line 9-9of Figure 8;

Figure 10 is a detail. perspective view showing the connection of one ofthe bulkheads with the pontoon bottom;

Figure 11 is an enlarged, perspective view showing a portion of a bottomchord in the plane of the section line l I-II of Figure 8;

Figure 12 is an enlarged. sectional View taken on the line lZ-IZ ofFigure 2;

Figure 13 is an enlarged sectional View taken on the line l3-I3-ofFigure 12; and

Figure 14 is an enlarged perspective viewtaken on the section line Ifl-l 4 of Figure 12.

A pontoon hull 2U (Figure 2) has bulkheads 2| 'connecting reinforcingvrelements 34 and to 24 running from side to side, fore and aft of themiddle of the pontoon; and bulkheads 25 and 26 extending from end toend. All bulkheads are rigidly united at the intersections. There is abuoyancy chamber in the pontoon between the bulkheads 22 and 23, but allof the other compartments formed within the hull by the bulkheads arepreferably flooding compartments for sinking the dry dock. The locationof the starboard wing wall section carried by the pontoon is indicatedat 28, and of the port wing wall section by the broken lines 29. Framingtrusses 30 extend parallel to the bulkheads 25 and 26 on both sides ofeach, with extensions at intervals beyond the bulkheads 2i and 24running out to the ends of the pontoon as seen in Figures 1 and 8. Thesetrusses occupy most of the interior of hull, but are supplemented by apair of trusses 36a and extensions Sia (Figures 1 and 2) one at each ofthe longer sides of the pontoon.

The trusses 39 rigidly connect the transverse bulkheads 2l and 22 in theport half of the pontoon and the bulkheads 23 and 2d in the starboardhalf of the pontoon. Beyond the bulkheads 2! and 24 the extensions areindicated at 3l; these are not so close together as the trusses 3i). Inthe illustrated embodiment, every other one of the trusses 36, withreference to either of the bulkheads 25 and 26, has an extension 3l.Each of these trusses and extensions, and each side truss 30a and itsextension 3Ia form a single continuous reinforcing truss member. Thetrusses 3!) may be continued across the buoyancy chamber at a suitablenumber of points, if desired; see the broken lines between the bulkheads22 and 23 in Figure 2.

The bulkheads 25 and 26 are continuous and traverse the width of thebuoyancy chamber between the bulkheads 22 and 23. Between the latterbulkheads the hull is further reinforced and braced as set forth belowto give it the strength required. When the pontoon is assembled side byside with otheri pontoons to make a dock, as set forth in myabove-mentioned aplplication, with the bulkheads 2|, 22, 23 and 24 andthe wing wall sections on each of the pontoons all in alignment withthese bulkheads and wall sections of the other pontoons; and a ship ismoved in for repairs; the weight of the ship is borne upon keel blocks,indicated at K, Figure 2 on the floor or deck of the dock, in themiddle; and bilge blocks. indicated at B set up near the .lines of thebulkheads 2l and 24. Each row of blocks bears about one-third of thetotal weight of the vessel.

I shall first describe the outer trusses 33a and the extensions Slawithin the pontoon at each long side of the hull, parallel to thebulkheads 25 and 26, as shownin Figure 1. This sectional viewillustrates deck plating 32 and a top beam 33, also parallel to thebulkheads 25 and 26; and reinforcing elements 34 arranged crosswisethereof, The pontoon has bottom plating 36 with similar elements 31 andbottom chords or beams 38, extending in the same direction as beams 33.The beams 33 and 38 and the members 3!! and 31 lie between the bulkheads2i and 22, 23 and 24. Between the extremities of the pontoon and thebulkheads 2l and 24these beams are extended in somewhat modifiedcross-sectional form as shown at 33 and 38' (Figure l) and the Y 3? arein the same part of the pontoon. At the 'very ends, fore and aft, eachof the beams 38' widens outl into a broad web and runs up to the deck,as shown in Figure 1 at 38a.

Along these sides, further, between bulkheads 2| and 22, 23 and 24, andbeyond the bulkheads 2| and'24, uprights 33 unite the upper beams 33 andtheir extensions 33'; at their junctions with the upper members 34 and3-t; to the lower beams 33 and t8 at their points of intersection withthe lower members 3l and 3l'. Alternate uprights 33, which are I-shapedin cross-section, of trusses a and all uprights in extensions Stu areconnected with the top beam 33 and 33 and lower beams 38 and 38 nbydiagonal braces 59. These braces 4Q are made fast to the uprights 39, atpoints midway between the upper and lower ends thereof, by `gussetplates 4|, to form frames that are K-shaped. All of the uprights 39 areconnected at the same points with horizontal braces or channel .beams42, which join the K-frames of each truss at their centers. vBeams 42are also affixed to the bulkhead at the buoyancy chamber and to a plate33h at the edge of the web 38a.

There are horizontal stiifening members or ribs 44 secured to thebulkheads 2|, 22, 2?, andZll. A rectangular coaming 4t is secured on thedeck of the pontoon at each end and serves as the support for thesection of the wing wall which is there mounted on the pontoon. Eachcoaming extends across the pontoons full width and its two long sideslie in approximately the plane of the outermost uprights Y33, and theplane of the nearest bulkhead 2| or 24.

On one face of each of the bulkheads 22 and 23 at each side of themiddle of the pontoon are vertical .stilening ribs 23a, T-sha-ped incrosssection, presented to the bulkheads 2| and 24 and anchoring theadjacent ends of the channel `beams Y42. These ribs are welded-to thedeck and bottom beams 33 and 38. At their junction with the latter aregussets lila to which the lower ends of the adjacent diagonal ,bracestil are welded. Between each of the bulkheads 22 and 23 and the outerones 2| yand 24, the uprights '3S and braces 4B are illustrated asproviding four K- frames, starting at the former and ending at thelatter; and two more such frames beyond bulgheads 2! and 24. All diagonmbraces welded to the faces of Athe plates 5i `which are m tum weldedalong one edge to the edges oi the anges or" uprights 3s; and the outerfaces of the bulkheads 2i and are also reinforced in the planes of thetrusses 3io by `Vertical ribs 3.9 comprising angle beams welded along`their outer edges, as shown in Figure l.

Figure 4 shows the connection between the diagonal braces t@ and thebea-ms 3,3 and .3S and their extensions. Each vdiagonal brace do isangle member and attached to the top of *ne beam shown for example atwith one its flanges Vertical and in the vertical plane of the web ofthe beam. The brace is bevelleo. with the top of the beam, and the otheror flange of the. brace rests on thetopoi the b o.

An extension it is welded to the web and flange of the beam and to theend of the ange of the brace in such a position that it forms, ineiiect, a continuation of the other or side flange of the diagonal brace4i).

A splice plate 45 has its upper portion welded edgewise to the outsidecr back ei the vertical flange of each diagonal brace 40, and its lowerportion welded to the remaining face of the vertical web of the beam 33.The `cut-out or recessed portions El l(Figure 3) of the parts ci and 48are for fitting the edges of the flange 6 of the beam V38. The topbraces are similarly secured at -their upper ends,

Between each of the outer bulkheads 24 and 2|, and the ends of thepontoon, the two additional `K-frames along the `sides have theircenters in similar uprights; and are attached to the beams 33 and 38' inthe saine way; :except that the diagonal braces of the first are madefast at their ends near the deck bottom beam extensions to the upright`reiirforceinents 33' upon said bulkheads.- The channel beams @2 extendfrom said bulkheads through these two K-frames also and are joined, asalready stated, to the widened portions 38a of the beams at the ends ofthe pontoon. These beams are pieced at the bulkheads 2| and 2Q, andsecin'eiy welded thereto.

Thus a complete truss or girder made up of K-frames extends from eachbulkhead i2 and 23 out past the bulkheads 2| or 24 to the two ends ofthe pontoon along either side.

Figure 5 shows the design and arrangement of these trusses Sla along thesides, beyond the longitudinal bulkhead 24; the plan beyond the bulkhead2| being the same. This View also f depicts the longer bulkheads 25 and26 and with stiffening ribs lil extending horizontally along same andtheintersecting bulkheads. Manholes such as appear at 5| .are provided nearthe lower end of the bulkheads 2| and 24 for access from one compartmentto another. When the dry dock pontoon is in use, each manhole 5| ispreferably closed by a plate, and each of the compartments is providedwith its own piping for flooding or pumping water from the compartment.Similar manholes are provided in the other bulkheads wherever needed.

The construction of the trusses Sil and the extensions 3! is bestillustrated in Figures 5, 6 and 8. The trusses 3l! include horizontalupper chord members made of beams 52 and lower chord members embracingbeams 53, connected together by upright beams .or columns 54 anddiagonal braces 5E. Each deck chord consists of two parallel beams 52,each bottom chord of similar beams Y53, extending from the bulkheads 22and 23 out to the bulkheads 2| and 24. They lie between and outside ofthe 'bulkheads 25 and 26. The vdiagonal braces 55 comprise opposed anglebars connected together by batteri plates 5l, The trusses all haveuprights 54 that are I-shaped in cross section. A section through thetrusses 30 is shown in Figure 6 to indicate how the uprights V54 areinserted at their ends between the beams 52 and 53 and united thereto;the braces 53 having their ends attached to these chords in the samemanner.

The braces 56 are omitted from Figure 6 for the sake of clearness. ButFigure '7 illustrates the manner in which the diagonal braces 56 of thetrusses 3b are connected with the uprights 54 at approximately themid-points of the latter, by means of gusset plates 53 welded to theflanges of the braces and uprights. The trusses 30 are cross-connectedwith one another by channel beams 43, welded to the outside surfaces ofthe anges of the uprights 54, with reinforcing plates 59 welded to theinside faces of the flanges and to the websof the uprights 51E in such aposition as to form, in effect, a continuation of the sides of thechannel beams 43. This construction gives the cross beams 43 the samestrength as if they were continuous, and at the saine time does notweaken the uprights 54 by cutting through their nanges. The beams 43join the centers of the K-framesfrom the channel beam 42 on one side ofthe pontoon to the channel 42 on the other and are rigid with thebulkheads 25 and 26 where they connect with same. These beams reduce thefree, e'lective span of all the uprights in the trusses by half, andreduces the amount of material otherwise needed. The construction of thetruss extensions 3| is similar to that of the trusses 36.

Figures 1 and 6 show the K-trusses 36 arranged relatively close togetherbetween bulkheads 2| and 22, 23 and 24; and Figure 5 shows how the trussextensions 3| are farther apart in the spaces between the bulkheads 2|and 24 and the ends of the pontoon. On either side of each of thebulkheads 25 and 26, the extensions 3| coincide with and arecontinuations of every second truss 36. In Figure 5 the positions of thetrusses 30 not extended are indicated by the plates 58.

.Figure 9 shows the bottom chord or beam structure of truss 36, betweenthe bulkheads 2| and 22, 23 and 24. Parallel structural members,preferably T-sections 6|, with the bottom plates 36 of the pontoonwelded to them, have the webs extending upward, and angle bars 62 arewelded to the upper edges of the webs of the T-sections 6|, theremaining flanges of the angle bars extending outward. The angle bars 62are connected by batten plates 63 at spaced points along their length togive a chord that is compound in structure. There are limber holes 64along the lengths of the T-sections 6| for the passage of water. The topchord with beams 52 is similar. The deck and bottom beams 52 and 53 arecrossbraced at the requisite number of points by ribs 34 and 31respectively, rigidly attached to said beams.

Figure 10 shows the union of the bulkheads and the pontoon deck andbottom plating. 'I'he bottom edge, for example, of the plating of thebulkhead 25 is shown welded to the upstanding web of a T beam 66. Thebottom plating is welded to the ilange of this beam. All the bulkheadsi.

may similarly be connected with the top and bottom plating of thepontoon hull.

Figure l1 shows the construction of the bottom chord of each trussextension 3| near the ends of the hull, at the places where it isintersected by bottom stiffening ribs 31a. These ribs are preferablyconstructed with recesses along their lower edges, to which are weldedthe bottom plates 35. The recessed or serrated edges also allow passageof water. of Figure l1 involving the parallel beams 53 differs fromFigure 9 in that at bars 6| take the place of the T-sections 6|, for inthe truss extensions 3| less strength is required. The beams 53' ofthese extensions are thus cross-braced by ribs 37a fastened thereto atvarious points.

Each upper chord of the truss extensions 3| comprises similar parallelbeams 52 between the bulkheads 2| and 24 and the ends of the pontoon ofslightly less height than the beams 52. These beams 52 are alsocross-connected along their edges, andcross ribs 34 of any suitable sizeand shape are attached between these beams.

In the trusses 3G, the bottom ends of thelower braces 56 are anchoredfurther between gusset plates 56a and 56o adjacent the lower beams 53,and welded to these plates. Reinforcing ribs 23' on the faces of thebulkhead 23 (and 22) connect the deck beams 52 to the bottom beams 53,and the plates 56a unite these ribs to the beams 53. The plates 55h areattached to the beams 53 and lower ends of uprights 55, and the lowerends of adjacent braces 56 and uprights 54 are between them and beams 53and attached to same. The braces 56 of the extensions 3| (ex- The bottomchord construction cept adjacent the bulkheads 2| and 24) are alsoreinforced by similar plates 56h at their junctions with upper and lowerbeams 52 and 53'. The braces 56 of the extensions 3| nearest to thebulkheads named are secured above and below with their ends partlybetween the beams 52' and 53', and reinforcing ribs 54a, attached to theadjacent faces of these bulkheads and uniting the deck beams 52 andbottom beams 53'. The uprights 54 and braces 56 as stated above, areenveloped at their ends by the beams 52 and 53 and welded to the innerface of the bars 6| and 62. The uprights 54 of the trusses 3| are weldedat their ends to the beams 52' and 53 at the flanges thereof; and theangle-bar braces 56 are welded to the inside faces of these beams, thesame as the braces 55.

The terminal K frames of trusses 3| at bow and stern, comprisingdiagonal braces 56' joined at deck and bottom to beams 52 and 53 aresecured at their adjacent ends to gussets 58' on partitions or auxiliarybulkheads 59 extending across the extremities of the pontoon. The beams52 and 53 terminate at these partitions and the remaining space isbraced.and divided as may be necessary.

Figure 13 illustrates the manner in which the six bulkheads areconnected with one another. Each of the bulkheads 25 (and 26) is ofcomposite construction and comprises plates or webs 68 between bulkheads2| and 22, 23 and 24, connected at one end with a solid column 69.

Each of the bulkheads 25 and 26 also includes plates 68 beyond bulkheads2| and 24, connected to the other sides of the solid columns 69. Such acolumn 69 is located at each junction of the bulkheads 25 and 25 withthe bulkheads 2| and 24. The bulkheads 2| and 24 are made up of platesor webs welded to opposite sides of the column 69.

Each column 69 is considerably thicker than the plates 66 but ispreferably provided with vertical stiiening ribs 'lil comprisingT-sections welded to one side. The portions of the bulkheads 25 and 26that extend through the buoyancy chamber are made of plates 'll muchthicker than the plates 68 in order to provide greater strength betweenthe bulkheads 22 and 23, which are subject to considerable pressure whenthe pontoon is flooded. For clearness the parts 69 and 'I9 are omittedin Figure 8.

Figure 14 shows the construction by which the bulkheads 25 and 26 arereinforced. In addition to the horizontal ribs 44 with serrated edgeswelded to the face of the bulkheads, there are upright flat bars orplates 'I3 welded to the bulkheads and the outer edge of each bar orplate 13 is stiiened by a T-bar 14 welded to the edge of plate 13. Thestiiening ribs 44 extend through openings in the plates 13. For the sakeof clearness, these ribs 44 have not been shown in Figure 8.

The horizontal channel beams 43 uniting the K-frames of trusses 3D and36a and extensions 3| and 3|a are also attached to the bulkheads 25 and26 in sections; one length having its end welded to the flange of theT-bar 14 and another length being connected with the other side of thebulkhead 25 by a gusset plate l5. There are plates or bars 'I1 betweenthe anges of the T- bars and bulkheads that form in effect continuationof the channel beams 43.

The construction at the sides of the pontoon between the outermosttrusses 30a and 3|a is indicated in Figures 5 and 6 but need not be L!detailed herein. These parts are reinforced and divided between thesides and the uprights 33; so as to support the outside plating andclose the pontoon, but the load stresses fall upon the trusses only.

All of the connections described herein are welded, but the invention isnot limited to welded joints and seams and some members can be used withrivets or other fastenings. Various changes and modications can be madeand some ofthe features oi the invention can be used without others.

In the trusses 32a and 3m the uprights Stall have the same dimensions;and so do the upper braces ll. The lower braces il are a bit lighterexcept the one nearest the end, which is of the same size as the topbraces. rhe lower braces are stressed more evenly by the buoyancy load;but at the outer end of the extension 31a the upward bending moment isgreatest. Hence the lower brace lli) at this point should be somewhatstronger.

As for the trusses 3.5, and 3i the uprights 5,4 and 5d are all a bitlighter than the upright/s 39, but those of the extensions 3l areheavier and stronger than in the trusses 3Q. The -iraines oi thesetrusses 3! and the extensions Si are also lighter than in the trusses35a and Sia, but are so designed that the braces 5t at the ends of thepontoon can well resist the upward bending i moment due to buoyancy; andthe braces in the extensions Sia at the bulkheads 2l and 26 are suitedto the weight loads of ship and wing wall section above and buoyancybelow. The upper braces in the trusses between the bulkheads 2i and 22,23 and 2G are lighter than in the trusses 3Go; and the remaining braces,upper and lower, in both trusses and extensions 3l, espe cially theupper and lower braces in the three remaining K-frames of the latterbetween the K-frames at the ends thereof and bulkheads 2l and 24 arelighter still than in extensions Bla because the stresses are less andthose due to the buoyancy loads are evenly distributed.

The central buoyancy chamber between the bulkheads 22 and 23, has arelatively light central bulkhead It and is traversed by the two longbulkheads 25 and 26. This chamber also contains room for machinery,crews quarters, storage and fuel space, etc. Between the bulkheads 22and 23 are reinforcing members 52A which are in line with the chordscontaining the members 52 and 52'; thus forming composite beams that arecontinuous from end to end of the hull. The waist of the hull containingthis chamber is iurther reinforced by iiooring and other members asrequired.

The unit stresses due to buoyancy load are reduced because the pontoonis lengthened beyond the wing wall locations. At the same time a moreecient beam effect is produced by the tapering ends of the hull.

It will be noted that the trusses S-Sa are all relatively closetogether. Hence only two bulkheads 25 and 25 running from end to end areneeded; and in a pontoon 250 feet long by 80 feet beam, for example,these bulkheads will be over 30 feet apart. The trusses stiften theother bulkheads and enable them to withstand the weight of ship and wingwall sections. Both weight loads and buoyancy loads are transmitted bythe trusses to the bulkheads 2l, 22, 23 and 24; and through these to thebulkheads 25 and 26. In the usual design of dry dock pontoon, with asingle central bulkhead parallel to the side walls,

transverse, bulkheads running in the sal-nedirec',v

tion as bulkheads 25 and 26 are added in such number that in a structureof the dimensions specified above, they will be only 8 feet apart. Thereplacement of most of these by K-trusses aflfords a great saving insteel, without loss of strength. The trusses make the bulkheads 2l to 2trigid; these in turn, especially Vin combination with the cross beams d3uniting the K-irames of the different trusses, stiften the bulkheads 25and 25 so as toobviate all risk of buckling, warping ory otherdistortion. These cross beams also brace the side plating. to the extentdemanded against the outside pressure of the water; the bulkheads 25 and25 and channel beams 52, and trusses 3l and Sig, also having the likeresult with respect to the outer plating at the ends. The general eiieetis to make the bulkhead, framework and deck and'bottom plating so rigidthat the bulkheadsvirtually become girders; with the deck and bottomplating serving as the flanges, and the bulkheads themselves as theWebs; and the cross,- beams d3 have the additional utility of so bracingthe K-frames at the centers that the spans o f the uprights 3.9, 5d and54 is only half their length. IThis too, increases thev strength and contributes to the general saving in materials oi construction.

As indicated in Figures 8 and 12, only the ex,- tension Si in the verymiddle of the pontoon will have five i -frames Those at each side willhave ewer because the hull is ship-shaped, as set forth in my co-pendingapplication for patent above mentioned. rThe transverse end bulkheads 59are of less height at the ends where they are attached to the bulkheads25 and 25 (Figure 12). The lower edges of these bulkheads curve upwardnear the extremities as Figures 8 and l2 illustrate. But the fourcross-beams 43 of the extensions 3l extend all the way across the endsfrom one side to the other.

The deck and bottom plating reinforcing ribs, beams, uprights, braces,bulkheads and all other members, are securely welded in their variousparts and in their respective positions to make the pontoon as strong aspossible at all points. rhe construction described is well adapted toattain all the objects of the invention.

Having described my invention, what I believe to be new and desire tosecure and protect by Letters Patent of the United States is:

1. In a hull for a dry dock the combination of trusses, each of whichhas a deck beam, a bottom beam, uprights connecting said beams, braces funiting said beams to points between the ends of the uprights, and beamsuni-ting said trusses to one another at said points.

2. A hull for a dry dock pontoon containing trusses, each of whichincludes a deck beam, a bottom beam, uprights between the beams,diagonal braces connecting the uprights at points intermediate theirupper and lower ends to said beams, a beam uniting said uprights of eachtruss at said points, and cross-beams connecting the .trusses togetherat said points.

3. A hull for a dry dock pontoon containing longitudinal bulkheads,transverse bulkheads intersecting said longitudinal bulkheads adjacentthe ends of said pontoon, vertical columns at the intersections, saidcolumns being of greater thickness than .the bulkheads and saidbulkheads being made up of sections that have their ends permanentlyconnected with said columns throughout the length of the latter, and atransverse bulkhead at each side of the middle of the 11 pontoonintersecting the longitudinal bulkheads, the latter being of greaterthickness between the last-named transverse bulkheads.

4. A hull for a dry dock pontoon having intersecting, rigidly connectedbulkheads and .trusses comprising K-frames crossing some of saidbulkheads and fixed thereto, said trusses being substantially parallelto the remaining bulkheads, and connected transversely to one anotheradjacent the midpoints of said frames.

5. A hull for a dry dock pontoon, comprising a pair of bulkheads betweeneach end and the middle of the hull, additional bulkheads extending fromend to end intersecting and united with the aforesaid bulkheads, andtrusses 4parallel with said additional bulkheads, said trusses unitingthe members of each pair of Ithe aforesaid bulkheads, and some of saidtrusses being extended beyond them towards each adjacent end of thehull.

6. The hull according .to claim 5, having cross beams at predeterminedpoints connecting said trusses and said additional bulkheads.

7. A hull for a dry dock pontoon having a pair of bulkheads between themiddle and each end, additional bulkheads extending from end lto end andintersecting and united with both pairs of bulkheads, trusses comprisingK-frames between and along the outer sides of the additional bulkheads,said trusses connecting the aforesaid bulkheads of each pair together,some of said Itrusses extending out lto the adjacent ends, `and a beamconnecting the K-frames of 'some of the trusses together at the centersof the latter.

8. The hull according .to claiml 7, having cross 12 beams to connect thecenters of the K-frames of the trusses to .the additional bulkheads.

9. In a hull for a dry dock pontoon, the combination of parallel top andbottom beams arranged in pairs, bottom plates attached to the loweredges of said bottom beams, ythe upper edges of said plates havingout-turned iianges, stiffening ribs passing through said beams,transverse battens secured to said flanges, uprights secured to the topand bottom beams, and braces secured to the uprights and the opposedfaces of said pairs of beams.

10. A hull for a dry dock pontoon, having inside .trusses extending sideby side, from the middle towards the ends of said hull, bulkheads spacedfrom the ends of the pontoon and intersected by said trusses, some ofsaid trusses being shorter and some longer than the remainder, thelonger projecting beyond said bulkheads, the shorter .trussesterminating at said bulkheads and short of said ends.

11. A hull for a dry dock pontoon, having trusses within the hull, saidtrusses extending side by side from the middle towards the ends,bulkheads spaced from the ends of the pontoon and intersected by saidtrusses, some of said trusses being shorter and some longer than theremainder, the longer projecting past said bulkheads, the shorter onesterminating at said bulkheads and short of said ends, and the longertrusses having relatively heavy portions at said ends to resist upwardbending moments.

FREDERIC R. HARRIS.

